Multiple axle vehicles such as medium and heavy-duty trucks and trailers exhibit a tendency to excessive wear at various points of suspension under the vehicle frame. This is due at least in part to the natural tendency for the axles to remain moving along a straight path, tangent in relation to a curve being turned. Forces are developed as the vehicle turns that urge the axles toward radial orientations. These forces strain the suspension-frame mounting bushings and cause premature wear.
It remains desirable though to allow maximum vertical travel of the wheels relative to the vehicle frame. Such movement should be taken up by the suspension rather than being transmitted directly to the frame.
The problem is then how to limit or stabilize the axles horizontally while allowing relatively free vertical motion. Various developments have been made for stabilizing tandem axles against torsional motion under braking loads. When brakes are applied, the axles have a tendency to twist or rotate about their axes.
Rigid struts or torque bars as shown in U.S. Pat. Nos. 2,999,695 to Bixby, or 3,313,369 to Whitehead longitudinally extend between brackets and frame at the center of the axles. Rigid torque bars serve their intended purpose to stabilize the axle against torquing but have little resistance to angular horizontal motion. In fact, the torque bar mounts themselves suffer the same undue wear from forces that tend to reposition the axles radially to the centers of turns.
The problem is more directly addressed by Joseph Schmitz who discloses a twin axle tracking system in U.S. Pat. No. 3,162,463. The Schmitz system is a complete tandem suspension involving rigid connector members extending from axles to a frame member between the axles. The remainder of the suspension is designed so the axles are allowed to swing to radial positions relative to the centers of encountered curves. The solution represented is thus to replace an existing suspension and axle assemblies with an assembly that will allow the axles to shift horizontally under the frame.
It remains desirable, however, for a stabilizing system that can be easily retrofitted to existing tandem axle-suspension vehicles, and that will hold the existing axles against angular horizontal motion.
U.S. Pat. No. 3,199,892 to Boys discloses a vehicle spring suspension that deals primarily with the torquing problem involved as discussed above. The solution offered by Boys, however, differs from the rigid connectors disclosed by Whitehead and Bixby in that extensible cylinders are used to interconnect the axle and frame members. The cylinder is actuated in conjunction with the vehicle brakes to prevent torsional movement of the axle. This represents an adequate solution to the brake torsion difficulty often experienced in trailers having wheel brake assemblies, but does not deal with the problem of horizontal forces applied during turning.
Of the above disclosed references, none show or suggest an adequate solution to the problem of providing stabilization of multiple axles against horizontal forces encountered in turning while permitting relatively free vertical motion thereof. Furthermore, none provide or suggest a solution that will enable use of existing axle and suspension components with such stabilization.